Throughout the summer months, London's Royal Opera House is buzzing. The main auditorium is bumper-to-bumper with opera and ballet buffs, and the front-of-house - the box office, restaurants and champagne bars, as well as the Vilar Floral Hall - are filled with visitors from all over the world.

Christopher Millard, the House's director of press, is not surprised. The Opera House is home to the UK's flagship opera and ballet companies as well as many visiting troupes, such as the Kirov, and since its redevelopment in 1997-1999, it has become a big attraction for both British and overseas visitors.

Mr Millard estimates that in its first full season (1999/2000) since redevelopment, 196,000 people visited the Opera House's public spaces, while 520,000 bought tickets for both the main auditorium and the two smaller theatres (the Clore Studio Upstairs and The Linbury Studio Theatre). Of those, a large part - some 20 per cent - were purchased by overseas visitors.

"The Royal Opera house is a key building in London's West End," says Mr Millard. "Since redevelopment, we have seen a huge increase in the number of day time walk-throughs, many of whom are visitors to the UK."

The Opera House is not unique. London's lyric theatres, those that present musical theatre, opera, drama and dance, are full of visitors in the prime summer months, as figures from the London Tourist Board's survey of overseas visitors show. In 1996 (the latest figures) tourists cited the theatre as one of the main reasons for visiting the city.

One-fifth of London theatre-goers are from overseas, says the Society of London Theatre's Wyndham Report, prepared by Tony Travers of the London School of Economics (LSE) with Mori. What is more, overseas visitors spend far above the average during their visit to the capital. The 1999 International Passenger Survey reckons they spent £6.7bn.

"As a London attraction, the West End is one of the main reasons why the capital is a world class city," says Mr Travers. "It is a mainstay of the new British economy and a significant contributor to our balance of payments. Theatre attendance dwarfs those of most tourist attractions."

The Report estimated that in 1997 the economic impact of West End theatre to the UK economy was around £1.1bn. It produced tax revenues of some £200m and 41,000 jobs - 27,000 directly and 14,000 indirectly.

The same year its exports totalled £266m to £286m, comprising both visitor spending and profits flowing back to the UK from overseas production of British shows. The West End's contribution to the UK's balance of payments was £216m to £236m.

"The West End theatre industry is an economic powerhouse on which depend thousands of jobs and the well being of hundred of British companies," wrote Mr Travers. "It is also part of what gives London its unrivalled allure as a tourist destination."

Travel firms bringing cultural tourists to the UK agree. "The UK is a vitally important destination for our customers," says Christopher Clark, the president of New York-based Great Performance Tours. "London's operatic and theatrical scene is as high quality as any in the world. No city is more exciting in terms of the lyric arts."

Another UK cultural attraction with overseas pull is the Edinburgh International Festival. The annual event, comprising six concurrent festivals (International, Fringe, Film, Book, Jazz, Tattoo), attracts some 950,000 attendees during the few weeks of its duration each August. Of those, an estimated 500,000 are visitors, 16 per cent of which are from overseas. These overseas tourists on average, stay 11 nights in the city or its environs.

To meet overseas demand, the International Festival channels ticket sales through agencies in the US, as does the Royal Shakespeare Company also pursues.

The RSC estimates that some 15 per cent of its Stratford audience comes from overseas. It works with several tourism partners, such as Birmingham International Airport (20 minutes from Stratford), to tap this market.

Arts events outside Stratford and the capital cities, such as the Glyndebourne opera festival and the Aldeburgh music festival, report a smaller percentage of overseas visitors. Both explain this in terms of their location, while the city of Cardiff believes its tiny number of cultural tourists (1 per cent) is due to the absence of a significant venue.

However, the Wales Tourist Board expects this to change with the completion of the Wales Millennium Centre in Cardiff in 2003. It forecasts international visitors will take up 8 to 10 per cent of tickets.